=Aristotle’s Logic.= Aristotle felt that there must be a science of the methods of science; and so successful was he in its formulation that it has practically remained as he transmitted it. We are struck by the way in which he divided science into the special sciences, each with its well-defined field. It was perfectly natural that he should also, with his great power of abstract reasoning, discuss the body of rules for legitimate thinking. In science there must be an art of investigation, just as in rhetoric there is an art of persuasion. At an early period these logical writings were collected under the name _Organon_, because the Lyceum regarded them so intimately connected with scientific procedure as to be the instrument or “organ” of all knowledge. Certain parts of Aristotle’s _Organon_ are of doubtful genuineness. The important sections are the _Analytics_, a masterly logical groundwork of the conclusion and proof, and the _Topics_, which treats of the inductive methods of probability. Aristotle therefore made logic a preliminary and separate study, as it should be. It became the preface to his scientific work. We shall briefly discuss Aristotle’s logic, because it is an exemplification of his general philosophical principle. Among the subjects in the history of philosophy, logic is perhaps the only one that has had no internal history. Aristotle was the pioneer in the subject. He left it so finished that scarcely any changes of consequence could be made in it. The external history of the Aristotelian logic has, however, been notable. A portion of the _Categories_ and _De Interpretatione_ was most influential in the history of the Middle Ages. The _Logic_ had been misunderstood and misapplied by Aristotle’s own School, so that when it came into the hands of the Schoolmen it had acquired the reputation of being only an abstract formal logic. As thus interpreted it was used by the Schoolmen and attacked by the philosophers of the Renaissance. Such a view of Aristotle’s logic is unjust to the author. He had conceived logic in its wholeness to be the true method to be used in investigating practical scientific problems.